Per ‘build quality’: the Rigol ‘scopes are the heaviest, by far. GW Instek and Siglent ‘scopes are much lighter. Whether lots of metal is a good or bad thing probably depends on the application.
In terms of ‘finish’, they’re all pretty good. Not as good as old HP ‘scopes, of course, but then they aren’t anywhere near the cost of those beasts. Modern Agilent (Keysight) stuff has been ‘cost reduced’ somewhat, unfortunately.
Responsiveness — the lack thereof — is what makes the cheap Rigols awful, in my opinion. Try to adjust a trigger level, or even shift the vertical position, and watch the ‘scope struggle to comply — tedious when you need exact settings. The Siglent and GW Instek use much more capable processors so don’t have this responsiveness problem. A lot of people don’t seem to consider this to be an issue, however. Perhaps this newer Rigol has a better processor and thus improved usability.
Ideally, you would check each option out in person. Looking for at least a couple of YouTube reviews of each (beware those enthusiastic reviewers of everything) should give you some assurance as to what you’ll get.